1. Field of the Invention
The invention relates to a method of producing a ring member, and particularly relates to a method of producing a ring member used to form, for example, an endless metal belt (power transmission belt) of a continuously variable transmission.
2. Description of the Related Art
In general, when a ring member used to form an endless metal belt (power transmission belt) of a Continuously Variable Transmission (CVT) is produced, first, a sheet material is cut out of a coiled material. The cut-out sheet material is rolled into a cylindrical shape, and butt portions are welded. Thus, a cylindrical member is formed. A plurality of ring members is then obtained by cutting the cylindrical member in the direction perpendicular to the axis of the cylindrical member so that each piece has a predetermined width, i.e., by cutting the cylindrical member into ring-shaped pieces (e.g., refer to Japanese Patent Application Publication No. 2006-124757 (JP-A-2006-124757)).
The plane surface of a strip-shaped material pulled out from the coiled material generally has undulated edges as shown in FIG. 8. When each sheet material 4 is cut out, a strip-shaped material 3 is generally cut along a pair of section lines, for example, A1, A1; A2, A2; or A3, A3. The paired section lines are parallel to each other. In this case, a member 14 between the sheet material 4 and the sheet material 4 is treated as scrap, resulting in a poor yield rate and an increase in production cost. Each sheet material 4 cut out in the above manner has the pair of the opposing section lines, for example, A1, A1; A2, A2; or A3, A3. The opposing section lines of each sheet material 4 are joined to each other by butt welding. However, because squareness between an edge face S3 of the strip-shaped material 3 and each of the section lines A1, A2, A3, and the like is not achieved, when this sheet material 4 is formed into a cylindrical shape, the required accuracy of this cylindrical member cannot be obtained. In other words, both ends of the cylindrical member are uneven, or the edge faces of both ends are not parallel to each other. Therefore, both ends of the cylindrical member also need to be treated as scrap, resulting in further deterioration of the yield rate.